In conventional lens cutting optics of laser processing heads, the lens separates the beam guidance from the process gas chamber. The beam guidance of laser cutting machines is flushed with pure gas thereby providing protection from surrounding dirt particles (e.g., smoke from the cutting) and undesired gaseous impurities. The cutting process is mechanically and chemically supported by process gases, generally oxygen or nitrogen. The pressure in the process gas chamber during processing is several bars.
Conventionally, focussing mirrors, which are considerably more robust against soiling compared to transmissive lenses, have been used in CO2 laser welding systems. However, due to the use of such mirrors, the processing side and the beam guiding side are not separate. For this reason, the deflecting optics in the beam guidance can be soiled more quickly due to, for example, smoke produced through welding during the process.
The use of more robust mirror optics is desired for laser welding, which can be, however, difficult to realize due to the very high pressure differences between the atmospheres in the beam guidance chamber and on the processing side.
Hermetic separation between the atmosphere in the beam guidance chamber and on the processing side is conventionally provided by an additional plane window or by disposing a ZnSe window in front of a focussing mirror. This window builds up the pressure for the cutting gas, thereby also separating the beam guidance from the process gas side. In both cases, a transmissive element, sensitive to soiling, is employed. A ZnSe window has known weaknesses due to the temperature-dependent refractive index that can limit its field of application and that of the lens.
It is therefore desirable to develop a laser cutting head that offers a simple constructive separation between the beam guidance and the laser processing region and that can be used for laser powers of more than 10 kW.